This invention relates to plasma display devices, and more particularly, to protected electrodes for such devices.
Plasma or gaseous discharge devices are exemplified in U.S. Pat. No. 3,775,764, issued Nov. 27, 1973, to Jai P. Gaur; and U.S. Pat. No. 3,781,600 issued Dec. 25, 1973, to William E. Coleman and Clarence W. Kessler, both of which are assigned to NCR Corporation, the assignee of the present invention. Both of these patents are incorporated by reference herein.
Gaseous discharge devices which utilize the tranfer of trapped charges resulting from the discharge are now well known. In the physical construction of a device using this principle, an ionizable gas is contained within an enclosure which has a plurality of dielectric-coated transfer electrodes arranged parallel but offset from one another on opposite side walls thereof. The transfer electrodes are capacitively coupled to the ionizable gas by their dielectric coating. Typically, information is entered into the device via an input electrode which does not have the capacitive-coupling dielectric coating and is, thus, direct-coupled to the ionizable gas. That is, the device is serially addressed by applying a voltage of predetermined magnitude between the direct-coupled input electrode and the first or nearest opposite dielectriccovered transfer electrodes. These two electrodes form the first cell within the device. By the proper application of a potential on the electrodes, the gas in the cells, formed by successive pairs of nearest adjacent, opposite electrodes, is discharged and electric charge trapped on the coated walls of the electrode is used to transfer this gaseous discharge throughout the length of the device. Typically, information is erased via an erase electrode directly-coupled to the ionizable gas.
Typically, all the electrodes including the direct-coupled input and erase electrodes are coated with a thin layer of dielectric such as magnesium oxide for obtaining the characteristics of low operating voltage and stable life of the device. Unfortunately, contamination of the thin magnesium oxide coating over the input and erase electrodes frequently occurs due to sputtering of the electrode material during the heat treatment stage of manufacture of the panel. Similar contamination occurs also as the result of plasma discharge during use. Both sources of contamination alter the operating characteristics of the panel. Gold or gold alloy input and erase electrodes have stable life characteristics. The use of gold, however, has the disadvantage of high cost, and, because the transfer electrodes are not of gold, also requires the precise alignment of the separate input, erase and transfer electrode screenings.
The present invention provides a simple and economical solution to these problems.